This invention pertains generally to image processing techniques for aligning two images, and particularly to the apparatus and method for guiding a missile to a target using image processing.
In certain military operations it is important to launch a missile from an aircraft toward a specific target on the ground. Substantial military advantage can be obtained if the missile is capable of guiding itself to the target, thereby enabling the aircraft with its human pilot to stay out of the dangerous area around the target. To achieve such a capability, the missile must have access to targeting information and must be able to identify the specific target while in flight.
In one contemplated weapons system, both the aircraft and the missile are equipped with Synthetic Aperture Radar (SAR). Generally, SARs are well known. Suffice it to say here that a SAR mounted on a flying body makes an image of objects within a field of view on the underlying ground. The image might be represented in any of a number of ways. For images that are to be further processed by a computer, the image would most likely be represented by an array of digital words, with each word describing the intensity of radar reflections from a small area within the field of view. Alternatively, an image intended to be displayed to a human would resemble a picture of the ground area taken with a photographic camera.
It is desirable in some contemplated weapons systems for a human on the aircraft to designate a specific target in the image. The portion of the image adjacent the target becomes a reference image. Image processing apparatus on the aircraft would then pass the reference image to the missile. After launch, the missile would fly toward the target, forming its own SAR images. Processing on the missile would compare the reference image with the image from the missile. The missile guidance system could use the results of the image comparisons to steer the missile toward the designated target.
However, several problems must be overcome in order for the contemplated weapons system to function. One significant problem is that as the missile approaches the target, the viewing angle changes. Correspondingly, the SAR images formed by the missile in flight will differ from the SAR image formed by the aircraft as the missile gets further from the launch point. Therefore, the image processing must be relatively insensitive to changes in viewing angle. Another problem to be overcome is that the missile must be able to process the SAR images quickly so that the missile guidance system can respond quickly to needed course changes. Additionally, it is desirable for the image processing on the missile to require relatively simple hardware since the entire missile is expendable.